|Publication number||US8046522 B2|
|Application number||US 11/616,242|
|Publication date||Oct 25, 2011|
|Filing date||Dec 26, 2006|
|Priority date||Dec 26, 2006|
|Also published as||CN101606133A, US20080155178|
|Publication number||11616242, 616242, US 8046522 B2, US 8046522B2, US-B2-8046522, US8046522 B2, US8046522B2|
|Inventors||Alan W. Sinclair, Barry Wright|
|Original Assignee||SanDisk Technologies, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (91), Non-Patent Citations (16), Classifications (6), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
Reference is made to the following U.S. patent applications pertaining to direct data file storage in flash memory systems:
1) Ser. No. 11/060,249, entitled “Direct Data File Storage in Flash Memories” (publication No. 2006-0184720 A1), Ser. No. 11/060,174, entitled “Direct File Data Programming and Deletion in Flash Memories” (publication No. 2006-0184718 A1), and Ser. No. 11/060,248, entitled “Direct Data File Storage Implementation Techniques in Flash Memories” (publication No. 2006-0184719 A1), all filed Feb. 16, 2005, and related application Ser. No. 11/342,170 (publication No. 2006-0184723 A1) and Ser. No. 11/342,168 (publication No. 2006-0184722 A1), both filed Jan. 26, 2006;
2) No. 60/705,388, filed Aug. 3, 2005, Ser. No. 11/461,997, entitled “Data Consolidation and Garbage Collection in Direct Data File Storage in Flash Memories,” Ser. No. 11/462,007, entitled “Data Operations in Flash Memories Utilizing Direct Data File Storage,” and related application Ser. Nos. 11/462,001 and 11/462,013, all filed Aug. 2, 2006.
3) Ser. No. 11/196,869, filed Aug. 3, 2005, entitled “Interfacing Systems Operating Through a Logical Address Space and on a Direct Data File Basis.”
4) Ser. No. 11/196,168, filed Aug. 3, 2005, entitled “Method and System for Dual Mode Access for Storage Devices.”
5) Ser. No. 11/250,299, entitled “Method of Storing Transformed Units of Data in a Memory System Having Fixed Sized Storage Blocks,” and related application Ser. No. 11/250,794, both filed Oct. 13, 2005.
6) Ser. No. 11/259,423, entitled “Scheduling of Reclaim Operations in Non-Volatile Memory,” and related application Ser. No. 11/259,439, both filed Oct. 25, 2005.
7) Ser. No. 11/302,764, entitled “Logically-Addressed File Storage Methods,” and related application Ser. No. 11/300,568, both filed Dec. 13, 2005.
8) Ser. No. 11/316,577, entitled “Enhanced Host Interfacing Methods,” and related application Ser. No. 11/316,578, both filed Dec. 21, 2005.
9) Ser. No. 11/314,842, filed Dec. 21, 2005, entitled “Dual Mode Access for Non-Volatile Storage Devices.”
10) Ser. No. 11/313,567, entitled “Method and System for Accessing Non-Volatile Storage Devices,” and related application Ser. No. 11/313,633, both filed Dec. 21, 2005.
11) Ser. No. 11/382,224, entitled “Management of Memory Blocks that Directly Store Data Files,” and related application Ser. No. 11/382,228, both filed May 8, 2006.
12) Ser. No. 11/382,232, entitled “Reclaiming Data Storage Capacity in Flash Memories,” and related application Ser. No. 11/382,235, both filed May 8, 2006.
13) Ser. No. 60/746,742, filed May 8, 2006, Ser. No. 11/459,255, entitled “Indexing of File Data in Reprogrammable Non-Volatile Memories that Directly Store Data Files,” and related application Ser. No. 11/459,246, both filed Jul. 21, 2006.
14) No. 60/746,740, filed May 8, 2006, Ser. No. 11/459,268 entitled “Methods of Managing Blocks in Nonvolatile Memory,” and related application Ser. No. 11/459,260, both filed Jul. 21, 2006.
The following applications of Alan W. Sinclair and Barry Wright are being filed concurrently with the present application:
Ser. No. 11/616,236, filed Dec. 26, 2006, titled “System Using a Direct Data File System With a Continuous Logical Address Space Interface”; Ser. No. 11/616,231, filed Dec. 26, 2006, titled “Configuration of Host LBA Interface with Flash Memory”; Ser. No. 11/616,228, filed Dec. 26, 2006, titled “Host System with Direct Data File Interface Configurability”; Ser. No. 11/616,226, filed Dec. 26, 2006, titled “Managing a LBA Interface in a Direct Data File Memory System”; and Ser. No. 11/616,218, filed Dec. 26, 2006, titled “Host System that Manages a LBA Interface with Flash Memory”.
This application relates generally to the operation of a non-volatile memory system, such as re-programmable semiconductor flash memory, to store and transfer data with a connected host device, and, more specifically, to the management of data file objects therein.
In an early generation of commercial flash memory systems, a rectangular array of memory cells was divided into a large number of groups of cells that each stored the amount of data of a standard disk drive sector, namely 512 bytes. An additional amount of data, such as 16 bytes, are also usually included in each group to store an error correction code (ECC) and possibly other overhead data relating to the user data and/or to the memory cell group in which it is stored. The memory cells in each such group are the minimum number of memory cells that are erasable together. That is, the erase unit is effectively the number of memory cells that store one data sector and any overhead data that is included. Examples of this type of memory system are described in U.S. Pat. Nos. 5,602,987 and 6,426,893. It is a characteristic of flash memory that the memory cells need to be erased prior to re-programming them with data.
Flash memory systems are most commonly provided in the form of a memory card or flash drive that is removably connected with a variety of hosts such as a personal computer, a camera or the like, but may also be embedded within such host systems. When writing data to the memory, the host typically assigns unique logical addresses to sectors, clusters or other units of data within a continuous virtual address space of the memory system. Like a disk operating system (DOS), the host writes data to, and reads data from, addresses within the logical address space of the memory system. A controller within the memory system translates logical addresses received from the host into physical addresses within the memory array, where the data are actually stored, and then keeps track of these address translations. The data storage capacity of the memory system is at least as large as the amount of data that is addressable over the entire logical address space defined for the memory system.
In later generations of flash memory systems, the size of the erase unit was increased to a block of enough memory cells to store multiple sectors of data. Even though host systems with which the memory systems are connected may program and read data in small minimum units such as sectors, a large number of sectors are stored in a single erase unit of the flash memory. It is common for some sectors of data within a block to become obsolete as the host updates or replaces logical sectors of data. Since the entire block must be erased before any data stored in the block can be overwritten, new or updated data are typically stored in another block that has been erased and has remaining capacity for the data. This process leaves the original block with obsolete data that take valuable space within the memory. But that block cannot be erased if there are any valid data remaining in it.
Therefore, in order to better utilize the memory's storage capacity, it is common to consolidate or collect valid partial block amounts of data by copying them into an erased block so that the block(s) from which these data are copied may then be erased and their entire storage capacity reused. It is also desirable to copy the data in order to group data sectors within a block in the order of their logical addresses since this increases the speed of reading the data and transferring the read data to the host. If such data copying occurs too frequently, the operating performance of the memory system can be degraded. This particularly affects operation of memory systems where the storage capacity of the memory is little more than the amount of data addressable by the host through the logical address space of the system, a typical case. In this case, data consolidation or collection may be required before a host programming command can be executed. The programming time is then increased.
The sizes of the blocks are increasing in successive generations of memory systems in order to increase the number of bits of data that may be stored in a given semiconductor area. Blocks storing 256 data sectors and more are becoming common. Additionally, two, four or more blocks of different arrays or sub-arrays are often logically linked together into metablocks in order to increase the degree of parallelism in data programming and reading. Along with such large capacity operating units come challenges in operating the memory system efficiently.
The patent applications cross-referenced above describe memory systems that directly store data file objects in flash memory that are supplied by a host. This is different than most current commercial systems, where a continuous logical address space exists at the interface between the host and the memory system, as described above in the Background. With such a “LBA interface,” data of individual data file objects are most commonly present in a large number of memory cell blocks. The memory system does not associate data of the file objects supplied by the host, typically in clusters of multiple data sectors each, to individual data file objects. Rather, the host merely assigns unused logical addresses within the LBA interface to data being supplied to the memory system for storage that are not currently assigned to valid data. The memory system then assigns its various memory cell blocks to store the received data in ways that make the memory system operate efficiently but without knowledge of the data file objects to which the clusters belong. A typical result can be that data of individual file objects are fragmented into pieces that are stored in many different memory cell blocks.
In many of the patent applications cross-referenced above, on the other hand, the memory system receives the data file objects directly from the host, without going through an LBA interface, so that the memory system may allocate data of individual files to its memory cell blocks in a manner that improves its performance. For example, since the file to which the data belong is known, the memory system may limit the number of memory cell blocks in which any one data file is stored. Specifically, the memory system may restrict the number of memory cell blocks in which data of a file object is stored that also contain data of another file object. The fragmentation of file data can therefore be controlled. This minimizes the volume of valid file data that must be relocated out of a common block to reclaim obsolete data space that has been created when a data of the second file stored in the block is deleted or modified. This results in significantly improved performance and endurance over the life of the flash memory system.
Such improved performance and endurance may also be realized if the direct data file management system is implemented in the host instead of the memory system. An LBA interface may still exist between the host and the memory system. But rather than allocating file data in clusters to this single contiguous logical address space, file data are allocated to blocks of logical addresses within this space that correspond to physical blocks within the memory system. The file data management techniques described in the patent applications cross-referenced above to be implemented within the flash memory system with respect to physical memory cell blocks are instead carried out within the host with respect to logical blocks of contiguous addresses within the logical address space of the host/memory system interface. The memory system may then be a conventional one, with a LBA interface, as is currently commercially popular. Operation of the direct data file management system within the host may limit the number of logical blocks that contain data from more than one file, just as the direct data file system operating in the memory system limits the number of physical memory cell blocks that contain data from more than one file. Fragmentation of data of individual file objects among physical memory cell blocks is similarly reduced but is accomplished by managing blocks of the logical address space that is mapped into physical memory cell blocks.
Logical blocks at the LBA interface are therefore preferably mapped into physical blocks of the memory system that have the same data storage capacity and other similarities. Specifically, the logical blocks are configured by the host to appear to its direct data file system to be the same as the physical blocks would appear if the direct data file system was operating within the memory system. The characteristics of the physical memory blocks, information not normally supplied to the host, may be provided by the memory system upon its initialization with the host. The host then configures the continuous logical address space into blocks with characteristics that correspond to those of the physical memory and thereafter writes data to addresses within those logical blocks.
As an alternative, the direct data file system may, instead of being implemented in a host, be operated in the memory system with logical blocks defined across the continuous address space of a LBA interface of the memory system, in the same manner as described above. Even though part of the memory system, this direct data file operation is different than the examples described in the patent applications cross-referenced above. Instead of operating at the back-end of the memory system in a manner that allows the memory system to receive data in files that replaces the LBA interface, the examples described in the prior applications, the direct data file system may be added to the memory system in advance of the LBA interface and operated in the same manner described above as if in a host in advance of its LBA interface. Such a memory system may even be configured provide both the LBA interface and the file object interface through which it may communicate with a host that has either one or the other but not both types of interfaces. This is particularly convenient for use in memory cards that are made to be removably connected with many types of host devices.
As a further alternative, a removable mother card with processing capability may be provided with the direct data file system described above in order to add the direct file capability to a host that does not have it but which has a direct data file interface. The mother card, when connected with the host, then operates to provide a LBA interface at an output of the card to which a standard memory card with a LBA interface may be removably connected.
Additional aspects, advantages and features of the present invention are included in the following description of exemplary examples thereof, which description should be taken in conjunction with the accompanying drawings.
All patents, patent applications, articles, books, specifications, other publications, documents and things referenced herein are hereby incorporated herein by this reference in their entirety for all purposes. To the extent of any inconsistency or conflict in the definition or use of a term between any of the incorporated publications, documents or things and the text of the present document, the definition or use of the term in the present document shall prevail.
A typical flash memory system is described with respect to
Host systems that use such memory cards and flash drives are many and varied. They include personal computers (PCs), laptop and other portable computers, cellular telephones, personal digital assistants (PDAs), digital still cameras, digital movie cameras and portable audio players. The host typically includes a built-in receptacle for one or more types of memory cards or flash drives but some require adapters into which a memory card is plugged.
The host system 1 of
The memory system 2 of
A typical controller chip 11 has its own internal bus 23 that interfaces with the system bus 13 through interface circuits 25. The primary functions normally connected to the bus are a processor 27 (such as a microprocessor or micro-controller), a read-only-memory (ROM) 29 containing code to initialize (“boot”) the system and a random-access-memory (RAM) 31 used primarily to buffer data being transferred between the memory and a host Circuits 33 that calculate and check an error correction code (ECC) for data passing through the controller between the memory and the host may also be connected to the bus 23. A circuit 34 dedicated to encoding and decoding data passing through the controller may also be included. Such encoding includes compression and security encryption but most any type of data transformation may be performed in this manner. The dedicated circuits 33 and 34, when utilized, execute specific algorithms that could otherwise be executed by the processor 27 under firmware control. The controller bus 23 interfaces with a host system through circuits 35, which, in the case of the system of
The memory chip 15, as well as any other connected with the system bus 13, typically contains an array of memory cells organized into multiple sub-arrays or planes, two such planes 41 and 43 being illustrated for simplicity but more, such as four or eight such planes, may instead be used. Alternatively, the memory cell array of the chip 15 may not be divided into planes. When so divided however, each plane has its own column control circuits 45 and 47 that are operable independently of each other. The circuits 45 and 47 receive addresses of their respective memory cell array from the address portion 19 of the system bus 13, and decode them to address a specific one or more of respective bit lines 49 and 51. The word lines 53 are addressed through row control circuits 55 in response to addresses received on the address bus 19. Source voltage control circuits 57 and 59 are also connected with the respective planes, as are p-well voltage control circuits 61 and 63. If the memory chip 15 has a single array of memory cells, and if two or more such chips exist in the system, the array of each chip may be operated similarly to a plane or sub-array within the multi-plane chip described above.
Data are transferred into and out of the planes 41 and 43 through respective data input/output circuits 65 and 67 that are connected with the data portion 17 of the system bus 13. The circuits 65 and 67 provide for both programming data into the memory cells and for reading data from the memory cells of their respective planes, through lines 69 and 71 connected to the planes through respective column control circuits 45 and 47.
Although the controller 11 controls the operation of the memory chip 15 to program data, read data, erase and attend to various housekeeping matters, each memory chip also contains some controlling circuitry that executes commands from the controller 11 to perform such functions. Interface circuits 73 are connected to the control and status portion 21 of the system bus 13. Commands from the controller are provided to a state machine 75 that then provides specific control of other circuits in order to execute these commands. Control lines 77-81 connect the state machine 75 with these other circuits as shown in
A NAND architecture of the memory cell arrays 41 and 43 is currently preferred, although other architectures, such as NOR, can also be used instead. Examples of NAND flash memories and their operation as part of a memory system may be had by reference to U.S. Pat. Nos. 5,570,315, 5,774,397, 6,046,935, 6,373,746, 6,456,528, 6,522,580, 6,771,536 and 6,781,877 and U.S. patent application publication No. 2003/0147278.
An example NAND array is illustrated by the circuit diagram of
Word lines 115-118 of
A second block 125 is similar, its strings of memory cells being connected to the same global bit lines as the strings in the first block 123 but having a different set of word and control gate lines. The word and control gate lines are driven to their proper operating voltages by the row control circuits 55. If there is more than one plane or sub-array in the system, such as planes 1 and 2 of
As described in several of the NAND patents and published application referenced above, the memory system may be operated to store more than two detectable levels of charge in each charge storage element or region, thereby to store more than one bit of data in each. The charge storage elements of the memory cells are most commonly conductive floating gates but may alternatively be non-conductive dielectric charge trapping material, as described in U.S. Pat. No. 6,925,007.
The individual blocks are in turn divided for operational purposes into pages of memory cells, as illustrated in
A metapage formed of physical pages of multiple planes, as illustrated in
With reference to
The amount of data in each logical page is typically an integer number of one or more sectors of data, each sector containing 512 bytes of data, by convention.
As the parallelism of memories increases, data storage capacity of the metablock increases and the size of the data page and metapage also increase as a result. The data page may then contain more than two sectors of data. With two sectors in a data page, and two data pages per metapage, there are four sectors in a metapage. Each metapage thus stores 2048 bytes of data. This is a high degree of parallelism, and can be increased even further as the number of memory cells in the rows are increased. For this reason, the width of flash memories is being extended in order to increase the amount of data in a page and a metapage.
The physically small re-programmable non-volatile memory cards and flash drives identified above are commercially available with data storage capacity of 512 megabytes (MB), 1 gigabyte (GB), 2 GB and 4 GB, and may go higher.
Operation with a Logical Block (LBA) Memory/Host Interface
A common logical interface between the host and the memory system is illustrated in different forms in each of
Referring specifically to
Three Files 1, 2 and 3 are shown in the example of
When a File 2 is later created by the host, the host similarly assigns two different ranges of contiguous addresses within the logical address space 161, as shown in
The host keeps track of the memory logical address space by maintaining a file allocation table (FAT), where the logical addresses the host assigns to the various host files are maintained. The FAT table is typically stored in the non-volatile memory, as well as in a host memory, and is frequently updated by the host as new files are stored, other files deleted, files modified and the like. When a host file is deleted, for example, the host then deallocates the logical addresses previously allocated to the deleted file by updating the FAT table to show that they are now available for use with other data files.
The host is not concerned about the physical locations where the memory system controller chooses to store the files. The typical host only knows its logical address space and the logical addresses that it has allocated to its various files. The memory system, on the other hand, through a typical LBA host/card interface, only knows the portions of the logical address space to which data have been written but does not know the logical addresses allocated to specific host files, or even the number of host files. The memory system controller converts the logical addresses provided by the host for the storage or retrieval of data into unique physical addresses within the flash memory cell array where host data are stored. A block 163 represents a working table of these logical-to-physical address conversions, which is maintained by the memory system controller.
The memory system controller is programmed to store data files within the blocks and metablocks of a memory array 165 in a manner to maintain the performance of the system at a high level. Four planes or sub-arrays are used in this illustration. Data are preferably programmed and read with the maximum degree of parallelism that the system allows, across an entire metablock formed of a block from each of the planes. At least one metablock 167 is usually allocated as a reserved block for storing operating firmware and data used by the memory controller. Another metablock 169, or multiple metablocks, may be allocated for storage of host operating software, the host FAT table and the like. Most of the physical storage space remains for the storage of data files. The memory controller does not know, however, how the data received has been allocated by the host among its various file objects. All the memory controller typically knows from interacting with the host is that data written by the host to specific logical addresses are stored in corresponding physical addresses as maintained by the controller's logical-to-physical address table 163.
In a typical memory system, a few extra blocks of storage capacity are provided than are necessary to store the amount of data within the address space 161. One or more of these extra blocks may be provided as redundant blocks for substitution for other blocks that may become defective during the lifetime of the memory. The logical grouping of blocks contained within individual metablocks may usually be changed for various reasons, including the substitution of a redundant block for a defective block originally assigned to the metablock. One or more additional blocks, such as metablock 171, are typically maintained in an erased block pool. When the host writes data to the memory system, the controller converts the logical addresses assigned by the host to physical addresses within a metablock in the erased block pool. Other metablocks not being used to store data within the logical address space 161 are then erased and designated as erased pool blocks for use during a subsequent data write operation.
Data stored at specific host logical addresses are frequently overwritten by new data as the original stored data become obsolete. The memory system controller, in response, writes the new data in an erased block and then changes the logical-to-physical address table for those logical addresses to identify the new physical block to which the data at those logical addresses are stored. The blocks containing the original data at those logical addresses are then erased and made available for the storage of new data. Such erasure often must take place before a current data write operation may be completed if there is not enough storage capacity in the pre-erased blocks from the erase block pool at the start of writing. This can adversely impact the system data programming speed. The memory controller typically learns that data at a given logical address has been rendered obsolete by the host only when the host writes new data to their same logical address. Many blocks of the memory can therefore be storing such invalid data for a time.
The sizes of blocks and metablocks utilized in commercial memory systems are increasing in order to efficiently use the area of the integrated circuit memory chip. This results in a large proportion of individual data writes storing an amount of data that is less than the storage capacity of a metablock, and in many cases even less than that of a block. Since the memory system controller normally directs new data to an erased pool metablock, this can result in portions of metablocks going unfilled. If the new data are updates of some data stored in another metablock, remaining valid metapages of data from that other metablock having logical addresses contiguous with those of the new data metapages are also desirably copied in logical address order into the new metablock. The old metablock may retain other valid data metapages. This results over time in data of certain metapages of an individual metablock being rendered obsolete and invalid, and replaced by new data with the same logical address being written to a different metablock.
In order to maintain enough physical memory space to store data over the entire logical address space 161, such data are periodically compacted or consolidated (garbage collected) in order to reclaim a block that is added to a pool of erased blocks. It is also desirable to maintain sectors of data within the metablocks in the same order as their logical addresses as much as practical, since this makes reading data in contiguous logical addresses more efficient. So data compaction and garbage collection are typically performed with this additional goal. Some aspects of managing a memory when receiving partial block data updates and the use of metablocks are described in U.S. Pat. No. 6,763,424.
Data compaction typically involves reading all valid data metapages from a metablock and writing them to a new block, ignoring metapages with invalid data in the process. The metapages with valid data are also preferably arranged with a physical address order that matches the logical address order of the data stored in them. The number of metapages occupied in the new metablock will be less than those occupied in the old metablock since the metapages containing invalid data are not copied to the new metablock. The old block is then erased and added to the erased block pool in order to be made available to store new data. The additional metapages of capacity gained by the consolidation can then be used to store other data.
During garbage collection, metapages of valid data with contiguous or near contiguous logical addresses are gathered from two or more metablocks and re-written into another metablock, usually one in the erased block pool. When all valid data metapages are copied from the original two or more metablocks, they may be erased for future use. The occurrences of data consolidation and garbage collection increases as the fragmentation of the files being stored among different blocks increases.
Data consolidation and garbage collection take time and can affect the performance of the memory system, particularly if data consolidation or garbage collection needs to take place before a command from the host can be executed. Such operations are normally scheduled by the memory system controller to take place in the background as much as possible but the need to perform these operations can cause the controller to have to give the host a busy status signal until such an operation is completed. An example of where execution of a host command can be delayed is where there are not enough pre-erased metablocks in the erased block pool to store all the data that the host wants to write into the memory and data consolidation or garbage collection is needed first to clear one or more metablocks of valid data, which can then be erased. Attention has therefore been directed to managing control of the memory in order to minimize such disruptions. Many such techniques are described in the following U.S. patent application Ser. No. 10/749,831, filed Dec. 30, 2003, entitled “Management of Non-Volatile Memory Systems Having Large Erase Blocks,” now publication No. 2005/0144358 A1; Ser. No. 10/750,155, filed Dec. 30, 2003, entitled “Non-Volatile Memory and Method with Block Management System,” now U.S. Pat. No. 7,139,864; Ser. No. 10/917,888, filed Aug. 13, 2004, entitled “Non-Volatile Memory and Method with Memory Planes Alignment,” now publication No. 2005/0141313 A1; Ser. No. 10/917,867, filed Aug. 13, 2004, entitled “Non-volatile Memory and Method with Non-Sequential Update Block Management,” now publication No. 2005/0141312 A1; Ser. No. 10/917,889, filed Aug. 13, 2004, entitled “Non-Volatile Memory and Method with Phased Program Failure Handling,” now publication No. 2005/0166087 A1; Ser. No. 10/917,725, filed Aug. 13, 2004, entitled “Non-Volatile Memory and Method with Control Data Management,” now publication No. 2005/0144365 A1;” Ser. No. 11/016,285, filed Dec. 16, 2004, entitled “Scratch Pad Block,” now publication No. 2006/0161722 A1; Ser. No. 11/192,220, filed Jul. 27, 2005, entitled “Non-Volatile Memory and Method with Multi-Stream Update Tracking,” now publication No. 2006/0155921 A1; Ser. No. 11/192,386, filed Jul. 27, 2005, entitled “Non-Volatile Memory and Method with Improved Indexing for Scratch Pad and Update Blocks,” now publication No. 2006/0155922 A1; and Ser. No. 11/191,686, filed Jul. 27, 2005, entitled “Non-Volatile Memory and Method with Multi-Stream Updating,” now publication No. 2006/0155920 A1.
One challenge to efficiently control operation of memory arrays with very large erase blocks is to match and align the number of data sectors being stored during a given write operation with the capacity and boundaries of blocks of memory. One approach is to configure a metablock used to store new data from the host with less than a maximum number of blocks, as necessary to store a quantity of data less than an amount that fills an entire metablock. The use of adaptive metablocks is described in U.S. patent application Ser. No. 10/749,189, filed Dec. 30, 2003, entitled “Adaptive Metablocks,” now publication No. 2005/0144357 A1. The fitting of boundaries between blocks of data and physical boundaries between metablocks is described in patent application Ser. No. 10/841,118, filed May 7, 2004, entitled “Data Boundary Management, now publication Nos. 2005/0144363 A1, and Ser. No. 11/016,271, filed Dec. 16, 2004, entitled “Data Run Programming,” now publication No. 2005/0144367 A1.
The memory controller may also use data from the FAT table, which is stored by the host in the non-volatile memory, to more efficiently operate the memory system. One such use is to learn when data has been identified by the host to be obsolete by deallocating their logical addresses. Knowing this allows the memory controller to schedule erasure of the blocks containing such invalid data before it would normally learn of it by the host writing new data to those logical addresses. This is described in U.S. patent application Ser. No. 10/897,049, filed Jul. 21, 2004, entitled “Method and Apparatus for Maintaining Data in Non-Volatile Memory Systems.” Other techniques include monitoring host patterns of writing new data to the memory in order to deduce whether a given write operation is a single file, or, if multiple files, where the boundaries between the files lie. U.S. patent application Ser. No. 11/022,369, filed Dec. 23, 2004, entitled “FAT Analysis for Optimized Sequential Cluster Management,” describes the use of techniques of this type.
To operate the memory system efficiently, it is desirable for the controller to know as much about the logical addresses assigned by the host to data of its individual files as it can. Data files can then be stored by the controller within a single metablock or group of metablocks, rather than being scattered among a larger number of metablocks when file boundaries are not known. The result is that the number and complexity of data consolidation and garbage collection operations are reduced. The performance of the memory system improves as a result. But it is difficult for the memory controller to know much about the host data file structure when the host/memory interface includes the logical address space 161 (
Direct Data File Operation
The different type of interface shown in
Comparing the file based interface of
When a new data file is programmed into the memory with the direct data file storage techniques, the data are written into an erased block of memory cells beginning with the first physical location in the block and proceeding through the locations of the block sequentially in order. The data are programmed in the order received from the host, regardless of the order of the offsets of that data within the file. Programming continues until all data of the file have been written into the memory. If the amount of data in the file exceeds the capacity of a single memory block, then, when the first block is full, programming continues in a second erased block. The second memory block is programmed in the same manner as the first, in order from the first location until either all the data of the file are stored or the second block is full. A third or additional blocks may be programmed with any remaining data of the file. Multiple blocks or metablocks storing data of a single file need not be physically or logically contiguous. For ease of explanation, unless otherwise specified, it is intended that the term “block” as used herein refer to either the block unit of erase or a multiple block “metablock,” depending upon whether metablocks are being used in a specific system.
With reference to
Principles of a Flash Optimized File System
The same idea is illustrated in a different form in
The Memory 2 of
The technique of mapping data of file objects to a logical address space is illustrated in a different manner in
It will be noted from
This restriction keeps low the amount of data relocation that may become necessary, for example due to data of the other file subsequently becoming obsolete. When that occurs, valid data of a given file is typically copied from the block containing obsolete data of another file into another block. By restricting the number of blocks the given file shares with data of another file, such data copy operations become less frequent. This improves the performance of the memory system.
It is a logical block 193 of the logical address space 161 that is mapped into the physical block 181. The logical block 193 is defined to have the same data storage capacity as the physical block 191, and is also divided into the same number of pages 201-204 as the physical block 191, each logical page having the same data storage capacity as each of the physical pages 195-199. That is, the granularity of the logical address space is preferably made to be equal to the data storage capacity of a physical memory page or metapage. Data are assigned addresses of logical pages within the logical block 193 in the same sequence as pages of data are written in the physical block 191. Writing of data at the beginning of the first page 201 of the logical block 193 is made to start at the beginning of the beginning of the first page 195 of the physical block 191.
In order for this coordination of logical and physical functions to be maintained, a host that makes the file-to-logical block translation needs to know the physical characteristics of the memory with which it is operating. These characteristics may be, in an example of a memory system using metablocks, defined by the following parameters:
With this information, the host can configure the logical block structure of its logical address space 161 to operate in the manner illustrated by
Further details are provided in this section of example implementations of the technique of mapping individual files to logical blocks of a continuous logical address space. Certain aspects of this have already been described with respect to the following functions that are essentially the same: the “Flash-Optimized File System” of
Much of what is described in this section for mapping files to logical block addresses utilize the same techniques of mapping files to physical memory cell block addresses that are described in the patent applications cross-referenced above. The primary difference is that the file mapping is being done across a LBA interface, such as by a host device, instead of bypassing the LBA interface by directly mapping the data files to physical memory blocks, as described in the prior cross-referenced patent applications. The physical memory block mapping techniques of the prior applications may alternatively be applied to map data file objects to logical blocks of a LBA address space, some examples of which are described herein.
In the description herein of logically mapping file objects, data are said to be “written to” or “programmed in” blocks of the LBA interface. These logical blocks, of course, do not actually store data, contrary to the physical memory blocks, so this refers to designating addresses of data to a particular logical block. Similarly, a logical block is said to be “erased” when no data are allocated to it. An “erased” logical block is one that does not contain addresses of data, so is fully available to have addresses of data assigned to it. Other logical blocks may be “partially erased,” meaning that a portion of the logical block is available to receive additional addresses of data.
General Operation of the Flash Optimized File System
When a new data file is to be programmed into the memory, the data are written into an unoccupied logical block beginning with the first location in the block and proceeding through the locations of the block sequentially in order. The data are programmed within the logical block in the order received from the host, regardless of the order of the offsets of that data within the file. Programming continues until all data of the file have been written. If the amount of data in the file exceeds the capacity of a single logical block, then, when the first block is full, programming continues in a second empty (erased) block. The second logical block is programmed in the same manner as the first, in order from the first location until either all the data of the file are allocated or the second block is full. A third or additional blocks may be programmed with any remaining data of the file. Multiple logical blocks or metablocks storing data of a single file need not be contiguous. For ease of explanation, unless otherwise specified, it is intended that the term logical “block” as used herein refer to either a logical block having the same capacity as a physical block minimum unit of erase within the memory system, or a multiple block logical “metablock,” which corresponds to a multiple block physical metablock that is typically erased together, depending upon whether metablocks are being used in a specific system.
The diagram of
A preferred way for the memory system to manage and keep track of the stored data is with the use of variable sized data groups. That is, data of a file are stored as a plurality of groups of data that may be chained together in a defined order to form the complete file. As a stream of data from the host are being written, a new data group is begun whenever there is a discontinuity either in the logical offset addresses of the file data or in the logical address space to which the data are being allocated. An example of such a logical address space discontinuity is when data of a file fills one logical block and begins to be written into another block. This is illustrated in
The amount of data being transferred through the host-memory interface may be expressed in terms of a number of bytes of data, a number of sectors of data, or with some other granularity. A host most often defines data of its files with byte granularity but then groups bytes into sectors of 512 bytes each, or into clusters of multiple sectors each, when communicating with a large capacity memory system through a current logical address interface. This is usually done to simplify operation of the memory system. Although the file-based host-memory interface being described herein may use some other unit of data, the original host file byte granularity is generally preferred. That is, data offsets, lengths, and the like, are preferably expressed in terms of byte(s), the smallest resolvable unit of data, rather than by sector(s), cluster(s) or the like. This allows more efficient use of the capacity of the flash memory storage with the techniques described herein.
The new file written to the logical address space in the manner illustrated in
So long as the host maintains the file of
An example of the insertion of a block of data 191 into the previously written file of
As an alternative to the insertion of data into an existing file that is illustrated in
To further illustrate the use of variable length data groups, a sequence of several write operations involving the same file is shown by
The file of
A second update to the open file is shown in
The offsets of the data of each file are preferably maintained continuous in the correct logical order after the file's creation or modification according to the preceding description. Therefore, as part of an operation to insert data into a file, for example, offsets of the inserted data provided by the host are continuous from the offset immediately preceding the insert and data already in the file after the insert are incremented by an amount of the inserted data. Updating an existing file most commonly results in data within a given address range of an existing file being replaced by a like amount of updated data, so the offsets of other data of the file usually need not be replaced.
The granularity or resolution of the data so stored may be maintained the same as that of the host. If a host application writes file data with a one-byte granularity, for example, that data may be also be represented in the logical blocks with a one-byte granularity. The amount and location of data within an individual data group is then measured in a number of bytes. That is, the same offset unit of data that is separately addressable within the host application file is also separately addressable within that file when stored in the flash memory. Any boundaries between data groups of the same file within a logical block are then specified in the FIT to the nearest byte or other host offset unit. Similarly, boundaries between data groups of different files within a logical block are defined in the unit of the host offset.
The term “sector” is used herein with large block memories to denote the unit of stored data with which an ECC is associated. The sector is therefore the minimum unit of data transfer to and from flash memory when such an error correcting code is generated by the controller of the memory system and stored with the data. A “page,” when referencing physical memory, is used to denote a unit of memory cells within a block. The page is the minimum unit of programming. A logical “page” within the logical blocks is one containing the same amount of data as the physical page. The term “metapage” is used to denote a page with the full parallelism of a metablock. The metapage is the maximum unit of programming.
It will be noted from
It may also be noted that in addition to the file data updates of
The file of
Garbage collection on a file basis also normally results in the formation of new and different data groups within the file being consolidated. In the case of
Reclaiming the blocks holding data of the file when in the state of
File Block Management
Certain types of logical blocks are recognized on the basis of the structure of file data stored in them. Each file with addresses in the continuous address space is then noted to be in one of a number of states, each file state being defined by the number and types of blocks in which data of the file are stored. When data are to be written for a file, its current state and permitted transitions from one state to another are preferably controlled to restrict the number of blocks containing data for a specific file that also contain data of one or more other files. This promotes the efficient utilization of the logical blocks and reduces the frequency of later reclaim operations necessary to maintain enough erased blocks for accepting new or copied data.
The core types of logical blocks recognized in this example that contain file data are as follows:
Another type of block is the “erased block”, where there are no data addresses in the block, so its full capacity is available to accept data. When the logical address space of the LBA interface is full or nearly full of data addresses, a pool of a specified minimum number of erased blocks is typically maintained by continuously reclaiming unused capacity that exists within the logical blocks that are being used.
A “fractal block” is a collective term that refers to a program block, a common block or a full common block. A fractal block for a file contains valid data of the file, together with either un-programmed storage capacity, valid data for other files, or both. A primary purpose of the techniques described herein is to minimize the number of fractal blocks in the address space by managing the type of active block that is designated to receive data of a file. This reduces the instances of garbage collection and data consolidation (block reclaim operations) necessary to be performed in the logical address space in order to maintain the specified minimum number of erased logical blocks. The rate at which data may be written into the memory is then increased since less time is taken for internal copying of data to reclaim fragments of unused capacity in previously programmed blocks.
Additional terms are also used herein to collectively describe other types of blocks:
The example of
Data of a file may be written directly into erased capacity of a partial block that already contains data of another file, rather than into an erased block, in order to make good use of unprogrammed capacity in this form. This is particularly useful when a known quantity of file data less than the capacity of a full block is to be written. Existing partial blocks are searched to find an amount of erased capacity that fits the known amount of data to be written. The number of pages (or metapages if the metablocks are being used) of data is compared with the number of pages of unprogrammed capacity in partial blocks. When unused erased space of a program block is programmed in this way, it is converted into a common block.
The file A is written in the example of
Although the examples of
It will be noted that logical blocks 665, 669, 671, 673 and 675 are fractal blocks. It is desired to minimize the number of fractal blocks occupied by data of any one file since their presence increases the likelihood of the need to reclaim unused capacity in them and thus adversely affect system performance. Unused erased capacity exists in partial logical blocks 665, 669, 673 and 675 but it may not be efficient to write new data from a host directly into this space unless the quantity of unwritten data for a file is known and that known amount matches the unused capacity of one of these blocks. It is most common that the amount of data from the host for a particular file is not known, so these bits of capacity are not readily filled. Data may therefore need to be moved from another block into the unused space during a reclaim operation in order to make efficient use of the memory capacity. Blocks 669, 671 and 675 contain data of more than one file, which means that when one of the files is deleted or its data stored in the common block becomes obsolete, data reclaim will likely be done to reclaim the capacity of the block occupied by addresses of obsolete data.
Therefore, in order to reduce the number of time consuming data reclaim operations, data of a particular file are allowed to be stored in only one, two or some other number of fractal blocks at any one time. In determining the number of fractal blocks to be permitted, the benefits of being able to use them are balanced against the adverse impact of having them. In the specific example described herein, data of any one file may be stored in two or fewer fractal blocks but no more. A process of designating a new active block to store data of a file is so constrained. One of a set of permitted file states is assigned to each file that is defined by the types of blocks in which data of the file are stored. When a new active block needs to be assigned for receiving data of a particular file, such as when an existing block becomes full, the type of block so designated depends upon the state of the file and, in many cases, also other factors.
Definitions of seven permitted file states 00-20 are given in the table of
File state transitions are subdivided into three classifications, depending on whether they are associated with programming data, with data being made obsolete, or with a reclaim block being selected. Permitted transitions in the file states due to a pending or completed data programming operation are illustrated in the state diagram of
Labels on the state transitions of
Most state transitions occur automatically when a block is allocated or a block becomes full. However, some of the defined state transitions also incorporate relocation of specific data from one block to another. The data is relocated as a single uninterrupted operation, and the state transition is considered to have occurred only after completion of the data relocation. Such transitions are designated “data transitions”. The table of
Partial blocks may be allocated as active blocks when the data to be written is of known length. In such case, the “best fit” partial block is selected from the population of partial blocks in the device. “Best fit” is defined as a partial block having an amount of erased capacity that the known amount of data to be written can efficiently utilize. In some cases, the “biggest” partial block may be selected as an alternative if a “best fit” partial block does not exist. This is the partial block with the highest amount of available unused capacity.
Labels on the state transitions of
The table of
When a block is selected as the reclaim block, it is no longer treated as a fractal block for files whose data exists in the block. This results in the file state transitions illustrated by the state diagram of
Details of the file state transitions due to the selection of a reclaim block are given in the table of
There are two alternative schemes for aligning data of files with the logical blocks of the continuous logical address space. In the case of the direct data file system operating on physical memory cell blocks, as described in the patent applications cross-referenced above, the start of a new file is preferably aligned to the beginning of an erased memory cell block. This may also be done when the direct data file system operating with logical blocks, as illustrated in
The table of
A file, such as one of the files A, B, or C in
Block reclaim is a process that is interleaved with the process of writing file data, wherein valid data is relocated from a block undergoing reclaim, in order to allow the block to be erased (all its capacity designated as unallocated) to reclaim unused capacity in the block. A block can be selected for reclaim for either of two reasons:
The benefit of the file-to-block mapping scheme shown in
A disadvantage of the mapping scheme of
An implementation of the scheme of
A benefit of the file-to-block mapping scheme of
A disadvantage of the mapping scheme of
Reclaiming Block Capacity
As described above, part of the block management includes reclaiming unused capacity in blocks for the storage of new data. This is not of particular concern when the amount of data stored in the memory system is far less than its capacity but a memory system is preferably designed to operate as if it is full of data. That means that blocks which contain only obsolete data, and other blocks that contain valid data but also have some obsolete data and/or unwritten pages, can be dealt with in a manner to reclaim this unused capacity. The goal is to utilize the storage capacity of the memory system as completely as possible, while at the same time minimizing adverse effects on performance of the system.
Any valid data in a block designated for a reclaim operation (source block) is copied into one or more blocks (destination blocks) with sufficient unallocated (erased) capacity to store the valid data. The destination block is selected in accordance with the block management techniques described above. The data of each file stored in the source block are copied to a type of block that is selected on the basis of the state of file and other factors, as described above. Examples of data copying between different types of files as part of reclaims operation are given in
The block 683 of
The block 691 of
As a result of each of the four specific examples of reclaim operations shown in
The deletion of a file from the memory also commonly causes data of the file in one or more fractal blocks, such as a common block or a full common block, to become obsolete. That block is then subject to a reclaim operation since the remaining valid data of another file will be less than the storage capacity of the block and can be a small amount.
A reclaim operation is shown in general terms by a flowchart of
The list(s) of such blocks changes constantly as data are written, updated, moved, deleted, and so forth. Changes that result in blocks changing their types to and from partial, obsolete and invalid cause the list(s) maintained by the step 701 of
In a step 703, a single reclaim block is preferably identified from those on the updated list(s) as the next in order to be reclaimed. If a partial or obsolete block, it is a source of valid data to be copied into another block referred to as a destination block. Several specific techniques that may be used to select the source block are described below.
A next step 705 of
If it is determined by the step 705 of
Returning to the step 707 of
In a first embodiment of the process of
This first embodiment of the process of
Therefore, in other embodiments of the process of
In these other embodiments of the process of
In a second embodiment of the reclaim block identification step 703 of
If there are no blocks on either of the invalid or obsolete lists, then a block on the partial block list is chosen in step 703 as the reclaim block. Although a partial block could be chosen to be that with the least amount of valid data, it is preferred to rank the partial blocks in a way that recognizes the benefit of their erased capacity. For this purpose, a “reclaim gain” can be calculated for each partial block, as follows:
reclaim gain=(S−kE)/V (1)
where S is the block size in terms of its total number of data storing pages, E is the number of pages of erased capacity into which data may be written and V is the number of pages containing valid data that needs to be moved to another block. A constant k is included to weight the positive effect of the erased capacity of the block but can be set at 1. As the value of kE increases, the resulting reclaim gain goes down. As the value of V goes up, the reclaim gain also goes down. The partial block with the highest value of reclaim gain is selected in the step 703 as the reclaim block. Other mathematical expressions can alternately be used to define a reclaim gain in terms of E and V that balance the detriment to system operation of containing valid data and the benefit of having erased capacity. The reclaim gain may be calculated each time there is a change in the block, such as each time data are written into its erased capacity, and stored as part of the information maintained by file directory or FIT.
This second embodiment is illustrated in
A third embodiment is shown by a flowchart of
A step 747 of
By adding the erased capacity quantity kE of the identified partial block to its valid data V before comparing with only the valid data V of the identified obsolete block, the process is biased in favor of selecting the obsolete block. An identified partial block with the same amount of valid data as an identified obsolete block will be retained since it is still has a potential use to store data in its erased capacity. Indeed, a partial block having an amount of valid data that is less than that of an obsolete block by an amount kE will be retained.
Returning to the step 745 of
The third embodiment may alternatively make use of only two lists. The first list is an obsolete block list that contains entries for blocks that contain obsolete data and no erased capacity. Rather than using a separate invalid block list as show in
The second list in this alternative to the third embodiment is a partial block list that contains entries for blocks that contain some erased storage capacity. The blocks may optionally contain valid data. Each entry in the list has a field containing a value defining the amount of valid data in the block to which it relates. The entries in the list are ordered according to the values in these fields. A block may be selected from the head (block with the least amount of invalid data) of either the first or second list by the technique of step 753 of
A table of
Although the various aspects of the present invention have been described with respect to exemplary embodiments thereof, it will be understood that the present invention is entitled to protection within the full scope of the appended claims.
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|U.S. Classification||711/103, 711/E12.008|
|Cooperative Classification||G06F12/0246, G06F2212/7202|
|Dec 26, 2006||AS||Assignment|
Owner name: SANDISK CORPORATION, CALIFORNIA
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Effective date: 20061218
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Owner name: SANDISK TECHNOLOGIES INC., TEXAS
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Effective date: 20110404
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